Spinning apparatus and method



Oct. 28, 1952 e. N. FLANNAGAN 2,615,193

SPINNING APPARATUS AND METHOD Filed April 6, 1949 IN V EN TOR.

Gordon Neel Flanagan BY A 'TTORNE Y Patented Oct. 28, 1952 SPINNING APPARATUS AND METHOD Gordon Neel Flannagan, Waynesboro, -Va., as-

signor to E. I. du Pont de Nemours & Company, Wilmington,'Del., a corporation of Delaware Application April 6, 1949, Serial No. 85,825

7 Claims.

This invention relates to improvements in the spinning of yarns from acrylonitrile polymers and more particularly to the production of such yarns having uniform denier.

Polyacrylonitrile and copolymers of acrylonitrile with other polymerizable substances, for example, vinyl or acrylic compounds, in which at least 85% by weight of the polymer is acrylonitrile, are recognized as possessing desirable physical and chemical properties including toughness and insolubility inand insensitivity to common organic solvents. While continuous filament yarns can generally'be prepared by dryspinning techniques using dimethyl formamide solutions of the acrylonitrile polymers, the ordinary method of passing the gaseous evaporating medium counter-current to the extruded polymer solution leads to unsatisfactory denier uniformity. This so-called updraft aspiration causes the filaments in the vicinity of the spinneret to wave in such a manner that the resultant yarn varies as much as 18% in short length denier measurements. The poor denier uniformity results in poor continuity in subsequent drawing operations, poor physical properties and uneven dyeing. Commercial fibers generally vary no more than 3-4% in short length denier measurements.

Most synthetic organic yarns are prepared using low boiling solvents, such as acetone, which are relatively easy to remove. However, acrylonitrile polymers which contain at least 85% by weight of acrylonitrile are insoluble in low boiling solvents and special solvents, such as those disclosed in U. S. 2,404,714-U. S. 2,404,727 inclusive, are necessary. The-dry-spinning of such solutions requires much higher temperatures than normally used in dry-spinning techniques and care must be taken to prevent excessive heating which leads to the formation of undesirable color in the yarn product. It is, therefore, desirable to use as high aspiration rates as possible to keep the temperature down and to increase the spinning speeds so as to effect greater economy. However, in updraft spinning using these necessary high aspiration rates, the turbulence of flow of the evaporative medium in the vicinity of the spinneret could not be readily avoided. Downdraft spinning alone in which the evaporative medium is introduced near the spinneret Y and removed at or near the bottom of the spinning cell still leads to unsatisfactory denier uniformity in the yarn produced.

Consequently, it is an object of this invention to-provide new apparatus and process for spinor A0 hing good quality yarns from solutions of acrylonitrile polymers. A particular object is to provide a process for preparing 'acrylonitrile polymer yarns having good denier uniformity. .A further object is to provide'an-acrylonitrile polymer yarn which can be subsequently drawn with a minimum number of breaks. A still further object is to prepare acrylonitrile polymer yarns having good uniform physical properties, including uniform dyeability. Other objects will become apparent in the following description.

The objectsof this invention are accomplished by extruding a solution of an acrylonitrile polymer ina volatile organic solvent through a spinneret into a heated cell and passing a gaseous evaporating medium concurrent with the extruded solution from a point above the spinneret to an exit at or near the bottom of the cell, the gaseous evaporating medium being passed through a means for converting it from a turbulent stream to a smooth stream, this means being, for example, an annular foraminous material, such as a perforated plate and. screens positioned in the spinneret head betweenthe gas inlet and the spinneret, the screens having a greater area than the cross-sectional area of the spinning cell.

In the figures, Figure 1 is a plan View and Figure 2 is a diagrammatic side elevation of the spinning head showing also its relation to the cell. This preferred spinning head In is used in theoperation of this invention to produce polyacrylonitrile yarns having highly acceptable short length denier uniformity (35% spread). The solution of the polymer is metered at con stant rate through the inlet I5 to spinneret and the filaments thus formed drop freely into the heated cell 30. The aspiration gas enters the head l0 above the spinneret 20 at through conduit and flows downward through a suitable gas heater and the perforated plate 10 and screen 80. The head I0 is attachable to cell 30 by any conventional means, as, for example, by a threaded joint or the apparatus may be in one piece.

In the dry-spinning of polyacrylonitrile from high boiling solvents, such as dimethyl formamide solutions, the filaments remain in the fiuid state for a considerable distance below the spinneret and are easily subject to deformation. When the heated air is aspirated countercurrent to the filaments, the velocity of the 'air in the cell causes the filaments to sway considerably. This filament motion, which could be easily seen at the sight box in the head of the cell, is proportional to the aspiration rate. In fact, the use of too high rates of aspiration causes the motion to increase to such an extent that spinning cannot be accomplished. When bafiies and screens, such as those shown in U. S. 2,252,684, are placed around the spinneret in an attempt to prevent this undesirable motion of the filaments, very little improvement is obtained and the resultant yarn still varies as much as 18% in short length denier measurements. This denier variation makes it impossible to market the yarn since it does not have good uniform physical properties and does not dye evenly.

While aspiration of the heated air concurrent with the filaments in the cell resulted in reduced motion of the filaments near the spinneret and a slight improvement in denier uniformity, the improvement is insufficient. A series of experiments showed that yarns having good denier uniformity could be made only by introducing the heated gaseous evaporative medium at a point above the spinneret and passing the medium through a foraminous means before allowing it to strike the filaments.

The improvements in denier uniformity obtained by using this novel aspiration system can best be illustrated by the following examples. In the experiments to be described, 360-denier, 20- -filament yarns were prepared from 20-21% solutions of polyacrylonitrile having an average molecular weight of 70,000 dissolved in dimethyl formamide. This viscosity of these solutions was approximately 55 poises at 125 C. The polymer solution was metered through a stainless'steel spinneret having a face diameter of 2.25 and containing 20 holes (0.11 mm. diameter). The filaments so-formed fell freely through a cell 12 long and 6 in diameter, unless otherwise specified. This cell was jacketed and heated with Dowtherm vapors which maintained a wall temperature of 253 C. Heated air was passed through the cell to remove rapidly the evaporating dimethyl formamide. The 20-filaments were converged near the bottom of the cell by means of a suitable guide and the resulting single strand of yarn was collected on a bobbin at 120 yds./min.

For the measurement of denier uniformity, a yarn sample was wound on a drum which was designed so that 9 cm. lengths could be cut off directly. Ten random 9 cm. lengths were cut off and weighed on a Roller-Smith weighing device. This was done four times on each of four spinning cakes. The per cent spread from the average denier for each experiment was obtained from these measurements. Statistical analysis of the results showed that by this method the precision (90% probable) at approximately 20% spread was :28, while at 8% spread the precision was 11.0 and at spread it was $0.5. This bears out the fact that the difierences in the denier uniformities, as expressed in the examples below, are real.

EXAMPLE I In this series of experiments, polyacrylonitrile yarns were prepared under the conditions described above. With the temperature of the head of the cell at 140 (3., air was introduced into the cell at difierent places in respect to the spinneret and aspirated through the cell at the rate of 52 lbs/hr. Before entering the cell the air passed through an Aerofin type heater maintained at 333 C. to maintain the gas around the spinneret at about 200 C. In the following table the denier uniformity as measured on nine centimeter lengths Table I Denier Uni- Experimeut ionmty In experiment A the air was introduced from opposite sides of the spinneret 20. Perforated plates holes on A centers) were mounted on each side of the spinneret, and 40-mesh screens were inserted beside each plate /2 toward the spinneret. In experiment B the screens and perforated plates were replaced by a single frustum shaped 40-mesh screen. In experiment C the heated air was introduced from above the spinneret at point 40. A perforated plate 10 containing j g holes, spaced 4 apart was placed between the air inlet and the spinneret. One-half inch below this plate, a IO-mesh screen was inserted. Experiment D diiTers from C in that no screen 80 or plates 10 were used.

It can be seen from Table I that all other conditions being equal, satisfactory denier uniformity is obtained only by introducing the aspiration air at a point above the spinneret and by properly dispersing the gas stream.

EXAMPLE II A number of experiments are combined in this example to illustrate the importance of the screen area. In calculating the screen area the area taken up by inlet I5 is considered. These experiments were carried out under identical conditions with those described above with the exception that the head of the spinning cell was maintained at C. and the yarn was spun at the rate of 250 yds./min. In these experiments, the head IE] of the spinning cell was changed both in size and in design. In every case, however,

' the aspiration air was introduced at the rate of 52 lbs/hr. above the spinneret at 40 and passed through the previously described perforated plate It and ill-mesh twill screen 80 placed between the air inlet and the spinneret. Table II gives the results of these experiments; the denier uniformity is expressed again as the per cent spread from the average denier of the yarns. This table illustrates that the ratio of the screen area to the cross-section area of the cell must be greater than 1 to produce polyacrylonitrile yarns having maximum denier uniformity by a dry-spinning process. The design of the cell head and the size of the cell in general may be varied provided the screening area is greater than the crosssection area of the cell.

Table II Denier Screen gn? 22; Uniformit Flat I 19 28 8 .do 27 2S 6 do. 4; 28 4.7 do..... 60 50 4 Frusturn 41 v 28 3.7

From the above results it is seen that the head it) may be round or square and the screens may be flat or frustum in shape. By the use of screens in the shape of a frustum the screen area may the rate of 60 lbs/hr. and downward through the cell. Its temperabe kept greater than the cell area even though the 'head diameter is not greater than the cell diameter. Other designs arealso possible. However,-as experiments E and F show. poor uniformityresults if the ratio of the screen area to the cell area is not greater than 1.

EXAIVIPLE III cell cross-section is 50 square inches. Kemp gas is introduced atthe top of thespinning head at It flows past the heater ture in the spinning head is about 225 C. The spinning solution passes through the spinneret 20 at a temperature of 135 C. Polyacrylonitrile yarns prepared in this manner have a denier spread of 4-5% consistently.

The gas is preferably introduced tangentially at 40 to induce a swirling motion at this point.

Perforated plate is rigid and contains, for

example, 9 holes, spaced apart. The perforated plate can be of any suitable design as long xasiit causes :a pressure drop in the gas flow equivalent to about three-eighths inch of water or sufiicient to introduce the gas uniformly into the spinning head. 'By suitable design, gas heater B0 and plate 10 may be incorporated into a single element. While the evaporative medium may .be heated outside the head, it is preferred for economy to heat the medium within'the head. In one embodiment a coil is placed in the head [0 situated around inlet IS. The air is thoroughly .heated by passing over and around this coil prior to its passage through the screen. Screen 80 may comprise a single screen or a number of screens in combination. If a single screen is used, it must be at least ZO-mesh and may be as fine as 400-mesh. Coarser screens than .20- mesh are applicable when more than one screen is used, e. g. three or four lO-mesh screens placed one upon another will yield results equivalent to a single 40-100 mesh screen.

In choosing a screening element, it is only necessary that there be a small pressure drop equivalent to about one-eighth inch of water across the screen. The screens serve to destroy the turbulence of the jets coming through the small holes of the perforated plate 10. The rate of aspiration of gas through the spinning cell affects the denier uniformity of the yarn roduced. The best denier uniformity is, of course, obtained at low aspiration rates. However, the aspiration rate necessary to produce good, nontacky yarn with a minimum of voids is dependent upon the denier of the yarn being produced. Thus for spinning heavy denier yarns, high aspiration rates are required to remove sufiicient solvent from the yarn so that the filaments do not stick together. The preferred aspiration rate when dry-spinning yarns from dimethyl formamide solutions of polyacrylonitrile is independent of the gas used and should be about 20 lbs. per pound of dry yarn produced. At high aspiration rates, the pressure drop across the plates and screens should be greater to smooth polymers, acrylonitrile/styrene copolymers, acrylonitrile/vinyl chloride copolymers, acrylonitrile/ vinylidene chloride copolymers, polyamides or cellulosic derivatives, such as cellulose acetate, other vinyl polymers, etc. from appropriate solutions. Further, while this invention has been described with particular reference to dimethyl formamide solutions of acrylonitrile polymers, solutions using any volatile organic solvent may be used. The term volatile organic solvent, as used in this specification, is meant to include those organic substances that are capable of forming stable homogeneous solutions with the acrylonitrile polymer or other polymers being spun and that can be distilled without decomposition at atmospheric pressure. Suitable volatile organic solvents for use with this invention in connection with acrylonitrile polymers include dimethyl formamide, dimethyl methoxyacetamide, N-formyl morpholine, N-formyl hexamethylene imine, butadiene cyclic sulfone, tetramethylene cyclic sulfone, p-phenylene diamine, and the mand p-nitrophenols. Likewise, solutions of the acrylonitrile polymers in those solvents disclosed in U. S. Patents ,Nos. 2,404,714 to 2,404,727 may be ,employedherein. Accordingly, any volatile organic solvent which forms the requisite polymer solutions and which has the desired stability may be used in the process of this invention.

Aspiration gases other than air are quite suitable for use in this process. In fact, less oxidation occurs and yarns having better color are produced when such inert gases as nitrogen, car- .bon dioxide, helium, argon, methane, producer gas and Kemp gas are used.

The denier uniformity is improved with increasing inlet gas temperature. This is in accordance with the theory that rapid solidification of the filaments as they leave the spinneret renders them less apt to deformation. However, it has been found that the eifects of aspiration rate and temperature on denier uniformity are considerably reduced when the area of the screen element in the head of the cell exceeds that of the cell cross-section, and the gas is introduced above the spinneret. On the other hand, these effects are accentuated when insufficient screening, i. e. when the ratio of the screen area to cell area is less than one, is used.

Other variables such as cell temperature and spinning speed were found to have very little or no effect on denier uniformity. In addition, the shape of the cell head is immaterial as long as the cross-sectional area of the screens exceeds the cross-sectional area of the cell. For practical purposes the ratio of the screen area to cell area should not be greater than four. Otherwise, the cell head would have to be extremely large in respect to the cell cross-section and the economics of a yarn producing plant would be adversely affected.

It can be seen from the description and examples of this invention that downdraft aspriation in combination with proper screening is necessary for the productionof uniform denier yarns from acrylonitrile polymers by dry-spinning techniques. The denier uniformity which results from the practice of this invention improves greatly the drawing continuity and the drawn yarns are much more uniform in physical properties and in dyeability. The dyeing uniformity is particularly improtant to the commercial exploitation of a synthetic yarn.

Any departure from the procedure described herein which conforms to the principles of the invention is intended to be included within the scope of the claims below.

I claim:

1. In apparatus for the dry spinning of yarns, a spinneret head attachable to a cell comprising a spinneret; a conduit to said spinneret; an inlet for directing an evaporative medium into said head tangentially to the walls of said head, said inlet being situated above said spinneret; a perforated plate and a screen situated between said spinneret and said inlet, said screen having a cross-sectional area greater than that of said cell.

2. Apparatus in accordance with claim 1 in which said screen is at least 2G-mesh.

3. A process for the conversion of an acrylonitrile polymer containing at least 85% acrylonitrile into a yarn having uniform denier which comprises extruding a solution of said polymer in a volatile organic solvent through a spinneret into a heated cell and passing a gaseous evaporative medium concurrent with the extruded solution from a conduit above the said spinneret to an exit near the bottom of said cell said conduit directing said medium tangentially to the walls of the head in which said spinneret is contained; and converting said gaseous medium from a turbulent flow to a smooth stream by passing it through a perforated plate and then through a screen, said plate and screen being positioned between the said spinneret and said conduit, said screen having a greater cross-sectional area than that of said cell.

4. A process in accordance with claim 3 which said solvent is dimethyl formamide.

5. A process in accordance with claim 3 in which said solvent is dimethyl formamide and said evaporative medium is aspirated at a rate of about 20 lbs/lb. of yarn produced.

6. Apparatus for dry spinning of yarns comprising a spinneret head comprising a spinneret; a conduit to said spinneret; an inlet for direct.- ing an evaporative medium into said head tangentially to the walls of said head and at a point above said spinneret; means for converting the turbulent flow of said evaporative medium into a smooth stream comprising a foraminous means for causing a pressure drop in the flow of said medium equivalent to about three-eighths inch of water and a foraminous element for causing a successive pressure drop equivalent to about one-eighth inch of water, said means and said element situated between said spinneret and said inlet.

7. A. process for the conversion of an acrylonitrile polymer containing at least acrylonitrile into a yarn having a uniform denier which comprises extruding a solution of said polymer in 9, volatile organic solvent through a spinneret into a heated cell; passing a gaseous evaporative medium concurrent with the extruded solution from a conduit above the spinneret to an exit near the bottom of said cell, said conduit directing said medium tangentially to the walls of the head in which said spinneret is contained; and converting said gaseous medium from a turbulent flow to a smooth stream by passing it through an annular foraminous material to effect thereby a pressure drop in the flow of said medium equivalent to about three-eighths inch of water and then through a second foraminous material to eifect thereby a successive pressure drop equivalent to about one-eighth inch of water, said materials being situated between said spinneret and said conduit.

GORDON N'EEL FLANNAGAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA IL NTS Number Name Date 2,252,684 Babcock Aug. 19, 1941 2,404,714 Latham July 23, 1946 FOREIGN PATENTS Number Country Date 725,421 France May 12, 1932 

